The traditional hook prosthesis has been the classic prosthesis for the amputee of a hand or forearm. Typically the hook or, more specifically, the split hook, consists of two hook sections joined at one end by a pivot. The terminal ends of the two sections are maintained in contact with each other by rubber bands wrapped around the two sections near the pivot point. A lever mounted on one of the hook sections and connected to a cable attached to the upper arm or shoulder is used to open the hook. The hook is typically lightweight, is capable of handling small objects, and provides maximum visibility. The hook is durable and provides a high pinch pressure while the force necessary to open it is relatively low. To its disadvantage, the hook is lacking in prehensile grip and natural appearance.
To overcome the lack of prehensile grip and poor cosmetic appearance of the hook, a hand prosthesis is often used, especially when the amputee is in public. In its simplest form the hand is merely a wooden, metal, or plastic model of a human hand. A basic improvement to this simple hand model has been the addition of controlled movement between the fingers and thumb of the hand resulting in prehensile grasp. In its basic form, the hand operates by a clamping action between the thumb and fingers. Typically, at least one finger is articulated and biased in opposition to an adjustable fixed thumb. U.S. Pat. Nos. 4,685,929 (Monestier), 4,685,924 (Massey), 4,291,421 (Massey). Generally the hand is much heavier than the hook, requires considerable more force than the hook to operate, and offers little in the precision necessary to handle small objects.
Because of the decided advantages and disadvantages of the hand and the hook, most arm amputees choose to purchase one of each. Although this seems like a ready solution to the problem, it has serious disadvantages: First, the process of detaching cables, switching devices, and reattaching cables is almost an impossible task for an individual with only one hand. In fact many amputees find this task so intimidating that they rely on others to do it for them. Second, the amputee must purchase and maintain two individual devices. In addition, the amputee does not have combined operating advantages readily accessible for spontaneous use as needed.